1. Field of the Invention
The present invention relates to a polymeric sol electrolyte and a lithium battery using the same, and more particularly, to a polymeric sol electrolyte having improved reliability and safety and a lithium battery using the same.
2. Description of the Related Art
Together with the recent development of miniaturized electronic devices, there is an increasing demand for small, lightweight batteries used to supply power to such devices. Although small, lightweight batteries, such as lithium batteries, have already been put into practice in the field of primary batteries, those primary batteries, which are not rechargeable, are restrictively used because they cannot be repeatedly used.
Secondary batteries that have been conventionally developed and used include Pb storage batteries, Ni—Cd storage batteries or Ni-MH storage batteries. However, it is quite difficult to achieve miniaturization of these batteries. Thus, lithium ion batteries that can be miniaturized and are capable of charging and discharging with high capacity, have recently gained commercial popularity for use in portable electrically powered devices and telecommunications devices, such as, for example, small-sized video cameras, mobile phones, notebook-type personal computers and the like. Lithium ion batteries have carbon compounds, capable of occluding or releasing lithium ions, for anode active materials, and lithium-transition metal oxides, such as LiCoO2, LiNO2, LiMn2O4, or LiFeO2, for cathode active materials.
However, when a lithium ion battery is overcharged, excess lithium ions are released from a cathode and migrate to an anode, so that the cathode and the anode become thermally unstable. When the cathode and the anode are thermally unstable, an organic solvent, particularly a carbonate-based organic solvent in an electrolytic solution, begins to decompose at 5 volts or higher. Decomposition of an electrolytic solution causes heat runaway, so that the battery may combust, swell or rupture. To solve these disadvantages, methods including addition of an overcharge polymerization additive to an electrolytic solution, and internal polymerization of a battery by adding a polymerizable material to an electrolytic solution, have been proposed . Examples of these methods are disclosed in Japanese Patent Publication No. hei 2000-58114, U.S. Pat. No. 6,033,797 and Japanese Patent Publication No. hei 10-241731.
Although the above-noted conventional methods are desirably used to protect batteries in an overcharge condition, deterioration in the reliability of a battery may occur, in view of cycle or retention characteristics.